It is necessary to first explain several concepts before starting to describe the background and the technical solution of the present invention:                to-be-transmitted data packets: data packets waiting to be sent in a sending device, comprising original data packets and data segments, wherein said to-be-transmitted data packets come from retransmission queue besides conventional transmission queue, and to-be-transmitted data packets in retransmission queue usually has a higher priority level;        transmission time interval (TTI): one kind of wireless transmission resource, and only after transmission time interval is allocated, will data packets in to-be-transmitted data packets be transmitted;        original data packets: data packets that have not been segmented, such as ARQ SDU;        component data packets: original data packets or data segments for constituting a to-be-transmitted data packet;        transmitted data packets: data packets being transmitted in one TTI;        data segments: a kind of data packets obtained from segmenting an original data packet or a data segment.        
It has been decided that automatic retransmission request (ARQ) is the most important function of RLC sub-layer in a system based on long-term evolution (LTE). One of the agreements about the ARQ is that segmentation or concatenation should be applied for the to-be-transmitted data packet according to the TB (Transmission Block) size, so as to make full use of the limited TTI.
It can be understood that, how to make the header portion of a transmitted data packet occupy number of bits as little as possible under the precondition of ensuring the receiver can receive and parse the transmitted data packet correctly is of critical importance to the limited TTI and the limited TB.
Although there are many structure definition schemes of transmitted data packet in the prior art, all of them contain relatively serious deficiencies. For example:                too many fields are needed to indicate one component data packet in the header of a transmitted data packet;        some of existing schemes do not work if segmentation happens to a data segment other than an original data packet;        some of existing schemes use one unnecessary “F” field to indicate each data segment;        the use of TSN or SSN causes large header overheads.        
Apparently, the header defined by the many definition schemes of transmitted data packet header in the prior art is far from optimal, and effective utilization of transmission time interval cannot be achieved.